Heterozygous knockout ofBile salt export pumpameliorates liver steatosis in mice fed a high-fat diet

The incidence of nonalcoholic steatohepatitis (NASH) is increasing worldwide, including in Asian countries. We reported that the hepatic expression of bile salt export pump (BSEP) was downregulated in patients with NASH, suggesting that BSEP is involved in the pathogenesis of NASH. To identify the underlying mechanism, we analyzedBsepheterozygous knock-out (Bsep(+/-)mice) and wild-type (WT) C57BL/6J mice fed a high-fat diet (HFD) (32.0% animal fat) or normal diet. We examined histological changes, levels of hepatic lipids and hepatic bile acids, and expression of genes related to bile acid and cholesterol metabolism. HFD-fedBsep(+/-)mice exhibited milder hepatic steatosis and less weight gain, compared to HFD-fed WT mice. The concentrations of total bile acid, triglycerides, and cholesterols were reduced in the liver of HFD-fedBsep(+/-)mice. Regarding hepatic bile acid metabolism, the expression levels ofFarnesoid X receptor(Fxr) andMultidrug resistance-associated protein 2were significantly upregulated in HFD-fedBsep(+/-)mice, compared to HFD-fed WT mice. Furthermore, several alterations were observed in upstream cholesterol metabolism in the liver. The expression levels of bile acid metabolism-related genes were also altered in the intestine of HFD-fedBsep(+/-)mice. In conclusion, HFD-fedBsep(+/-)mice exhibited significant alterations of the expression levels of genes related to bile acid and lipid metabolism in both the liver and ileum, resulting in alleviated steatosis and less weight gain. These results suggest the importance of BSEP for maintenance of bile acid and cholesterol metabolism. Further investigations of the involvement of BSEP in the pathogenesis of NASH will provide greater insight and facilitate the development of novel therapeutic modalities.